In certain space applications, it is desirable to use a vehicle that delivers a payload from an initial orbit to a final, higher orbit around Earth, or a trajectory that will send the payload beyond Earth. Such a vehicle may be a solar electric propulsion (SEP) vehicle that is capable of collecting and storing solar energy as electrical energy, and then using the electrical energy to power an electric propulsion system. To design a SEP vehicle capable of performing such a mission, vehicle designers are required to size the power and propulsion system appropriately. This sizing is influenced by the attitude and thrust vector of the vehicle, which necessitates an iterative design approach that quantifies the transfer time, the amount of propellant consumed, the number of on/off cycles of the electric thrusters, and other key vehicle design parameters. For SEP systems, the amount of power available at any given time is critical to effective modeling. The amount of power available to the thruster is calculated in situ.
Conventional SEP simulations exist, but specialize in trajectory optimization for interplanetary and primitive body science missions. For these science missions, such as Dawn and Deep Space I, the SEP part of the mission takes place in heliocentric space, where power produced by the vehicle's solar arrays is relatively constant, changing only very slowly with time as the solar arrays degrade or the distance from the sun changes (time constants on the order of months). Therefore, these computer programs do not contain detailed power system models since such models are not needed for these specialized applications.
However, for missions that spend significant amounts of time in the Earth's vicinity (i.e., starting in low Earth orbit (LEO)), detailed power system models, including solar array degradation, are essential. Conventionally, a methodology is employed to perform the required analysis that requires substantial time and manpower, and is extremely limited in modeling the entire vehicle as an integrated system. Such a conventional, iterative methodology 100 is shown in FIG. 1. Multiple software programs are utilized and decoupled from one another. These programs included a trajectory simulation program with simplified power and propulsion models and a power program with simplified trajectory data.
Neither program outputs data that can be used in a seamless manner as input into the other program. Both programs have to simplify the output data of the other program to be amenable as input data, which requires significant time and is error prone. This procedure takes weeks to complete a single iteration cycle and to result in somewhat consistent power and trajectory data. Additionally, the conventional methodology could not permit important trade studies to be performed. A preliminary vehicle design is simply not feasible using the old methodology because there is so much uncertainty in key vehicle design parameters. Accordingly, improved modeling, simulation, and control for SEP vehicles may be beneficial.